Intravenous treatment and other medical infusion procedures require introduction of a flexible catheter into the vascular system of a patient. Catheters of the in-dwelling type are left in place between periodic uses to reduce the number of traumatic incidents to the patient which would otherwise occur if a separate puncture were required with each use. A popular form of such catheters is the so-called "over-the-needle" catheter which consists of a removable stylet needle extending through a cannula and a female fitting secured to the proximal end of the cannula. The needle serves to pierce the skin and blood vessel or fistula of the patient, simultaneously positioning the distal end of the cannula therein, after which the needle is removed and discarded. U.S. Pat. Nos. 3,456,006 and 3,714,945 show examples of this type of catheter insertion unit.
It has been common practice to provide such catheter insertion units with a flashback chamber in fluid communication with the hollow needle so that, upon blood vessel entry by the needle, blood could flow into the chamber and thereby provide a visual indication to the medical attendant. Of course, before withdrawal of the needle, the tip of the cannula should be positioned sufficiently within the blood vessel; however, blood flashback from the needle only indicates that the needle bevel has entered the blood vessel and does not necessarily mean that the cannula also has entered the blood vessel.
It is therefore desirable to provide a separate flashback capability to signal when the cannula has entered the blood vessel. Needle flashback without cannula flashback would indicate that the cannula or whole unit should be inserted further. The occurrence of cannula flashback before or after needle flashback would indicate that no further insertion of the needle is necessary, thereby facilitating the accuracy of the procedure, minimizing discomfort to the patient, and reducing or eliminating damage to the blood vessel.
The catheter insertion units of the prior art, however, either have lacked this feature entirely, have been of unnecessarily complex and therefore costly construction or have suffered from other disadvantages. Although provision of side ports in the cannula to facilitate fluid flow is well known in the art, the catheter insertion units heretofore have been constructed to block the side ports before withdrawal of the needle, and have lacked any provision for a separate chamber in communication with the side ports for indicating cannula entry before removal of the needle. Moreover, even if separate chambers in fluid communication with the side ports were provided in the prior devices, the sideports have not been located sufficiently close to the distal catheter tip for flashback when the cannula entered a blood vessel.
A need has thus arisen for a simplified catheter insertion unit which provides an independent flashback indication of cannula entry into a blood vessel before removal of the needle.